The present invention relates to rotating flexible shafts having tips or ends adapted to engage mating elements of driving or driven members; and is particularly suited for use with, but not limited to wire wound flexible shafts.
Rotary shafts for transmitting torque typically have square ends adapted to engage square recesses of mating driving and driven parts. Rotary flexible shafts commonly used to transmit torque from a motor to adjust a seat in a motor vehicle, for example, are of wire wound construction and may, but need not, have helical square ends as shown in U.S. Pat. No. 6,464,588 to Rupp.
Typically the shaft and its male ends are steel and each female mating part is steel or plastic. To insure assembly will always be possible, manufacturing tolerances are set so that the maximum dimensions of the shafts are smaller than the minimum dimensions of the recesses in the mating parts. The interface is therefore always somewhat loose and can be noisy at operating rotational speeds.
It is known to add a layer of deformable material to the interface between the shaft ends and the mating recesses that dampens contact and reduces clearance, and thus functions to reduce noise. This noise reduction material, however, also has dimensional tolerances, and is subject to wear.
In European Patent Application Serial No. EP 1286065 of Otto Suhner AG (inventors Theo Eichenberger et al.) entitled Flexible Shaft With Noise Reducing Component, a flexible shaft for adjusting a motor vehicle seat has a surrounding casing, and noise is reduced by incorporating a relatively large diameter flocked yarn wire in the outer wire layer, so that the yarn helps to reduce noise due to contact between the rotating outer wire layer and the surrounding casing.
In U.S. Pat. No. 3,389,579 to Werner et al. entitled Shaft Guided In A Protection Tube, noise isolation between a flexible shaft and a surrounding protection tube is provided by adhering short elastic fibers to the outer surface of the shaft or the inner surface of the protection tube, to forma brush-like layer between the shaft and tube.
In U.S. Pat. No. 4,411,168 to Yoshifuji entitled Inner Cable, noise due to contact between a push-pull wire wound flexible cable and a surrounding conduit is reduced by winding a hollow elastic member on the cable core between wire teeth also wound on the core, the elastic member having a greater diameter than the teeth so that only the elastic member contacts the inner surface of the conduit, thus reducing noise when the cable is moved longitudinally.
In U.S. Pat. No. 4,849,038 to Burghardt entitled Method For Depositing An Interlining On A Pitched Cable For Reducing Friction And Noise, a filament flocked with abrasion resistant material is wound or deposited on a wire wound flexible shaft, interleaved with the wire of the outer layer of the shaft.
In U.S. Pat. No. 7,717,795 to Mellor, a deformable polytetrafluoroethylene sheath is applied over the ends of a flexible shaft to reduce noise and vibration due to friction and relative movement between the shaft ends and mating recesses.
The sum of the maximum dimensions of the noise reducing material and the maximum dimensions of the shaft must still be such that the shaft end and the noise dampening material can be installed in a mating part of the smallest possible manufactured dimensions. On the other hand, the sum of the minimum dimensions of the noise reducing material and the minimum dimensions of the shaft must fit within a mating recess of the largest possible manufactured dimensions with little or no clearance.
Therefore the noise reducing material must be such that it can be easily compressed or displaced during insertion of the shaft assembly into the mating recess, while exhibiting resistance to wear.
Accordingly, an object of the present invention is to provide a rotary flexible shaft that exhibits low rotational noise when coupled between driving and driven members.